The present invention relates generally to the field of air control dampers, and more particularly, to those air control dampers which are intended to regulate the volume of air passed along a duct or plenum, or through an opening, in which the damper is further adapted to prevent the passage of smoke or fire therethrough when the damper is in the closed position. For discussions of some of the problems encountered in the fire, smoke and air control damper field, please refer to my previously issued U.S. Pat. Nos. 3,381,601; 3,204,548; 3,605,603; and 3,899,156.
In particular, a suitable fire, smoke and air control damper should be easily operable to allow the flow of air therethrough in any of a desired number of predetermined settings between the closed and open positions of the blades with respect to the frame. With respect to the fire and smoke control aspect of such a damper, it is also important that a damper be capable of withstanding intense heat and/or air pressures which impinge on either side of the damper for substantial periods of time during a fire. Due to the extreme conditions to which such a damper is subjected, it is necessary to provide extremely strong blades and a very substantial frame which, together, form a tight, positive seal to effectively shut off the air duct, opening, or plenum. In fact, due to the deficiencies experienced by some practitioners in this field, folding blade fire dampers such as those illustrated in my previously issued U.S. Pat. Nos. 3,866,656; 3,866,657; 3,814,165; 3,401,734; 3,727,663; 3,327,764; and 3,273,632 have been utilized in order to overcome those deficiencies otherwise encountered by some devices utilizing a plurality of rotating blades, each of which blades must form a seal with an adjacent blade as well as the frame, which seal is sometimes prone to leakage in the event that extremely precise alignments and tolerances are not maintained. This problem has been aggravated by the fact that a smoke and fire damper must function effectively in a relatively dirty environment years after it has been installed.
Prior art rotating blade fire and smoke dampers have, therefore, incorporated extremely heavy materials which are not subject to easy bending or deformation in the presence of heat. The blades are mounted by distinct hinge or pivot means which are separately installed for the purposes of aligning each of the blades for rotational movement and to insure the interengagement of each blade with its adjacent blade to form a seal therebetween which does not open in the presence of heat or excessive pressures, such as those which might be encountered during a fire.
It is sometimes desirable to provide dampers with springs for forcing the blades of a folding blade or single blade damper to the closed position. My previously issued U.S. Pat. Nos. 3,899,156; 3,866,657; 3,814,165; and 3,401,734 illustrate various uses of springs in this regard. Spring closure devices, when they are used, are normally mounted at one end of the frame to pull curtain-type folding blade closures thereacross, or on one side of a single blade to cause that blade to engage a locking clip to lock in the closed position. Springs have not generally been used (in the absense of a locking device) to directly restrain the devices against fire since heat will tend to cause the spring to loose its strength, and thus its effectiveness.